The purpose of these investigations are to evaluate enhancement of resistance to Gram-negative bacillary infections by immunization with shared, cross-reactive antigens. Previous studies have demonstrated that both active and passive immunization of animals with antigen of the basal, core portion of lipopolysaccharide (Re mutant of S. minnesota) afforded significant protection against infection with heterologous bacilli and heterologous LPS. Similarly, patients with high titers of antibody to the Re mutant at the onset of bacteremia were shown to experience shock and a fatal outcome during Gram-negative bacteremia only 1/3 as often as patients with low titers of antibody. The present studies will continue immunization of volunteers with the Re mutant in an attempt to develop a vaccine preparation which can be tested for its effectiveness in preventing or ameliorating the severity of Gram-negative bacteremia in hospitalized patients. Other investigations will evaluate antibody titers in the large volume of plasma from blood bank blood supplied annually to the Biologics Division of the Laboratories of the Massachusetts Department of Health. If sufficient quantities of high titered plasma are found, factors involved in the use of such plasma in the treatment of Gram-negative bacteremia, as successfully accomplished by Braude et al, will be evaluated. Investigations to identify the immunodeterminant responsible for the induction of protective antibody and attempts to prepare an artificial immunogen will be continued.